Cathode heater arrangement for vacuum type display devices

ABSTRACT

A control circuit for controlling the symbols displayed by a plurality of lamp indicators, each having a cathode and a plurality of phosphor-coated anodes. The control circuit is adapted to control the showing of symbols when similar anodes in all the display devices are connected to a common supply conductor. During the showing of any symbol, the electronemitting cathode is temporarily disconnected from its power supply by a series transistor. This type of control circuit is particularly adapted to the showing of digital information provided by a computer circuit. The circuit does not employ resistors which produce excessive heat and power consumption.

United States Patent Inventor Francis A. McGuirk, Jr.

. Chatham, NJ. Appl. No 828,558 Filed May 28, 1969 Patented Jan. 5, 1971 Assignee Wagner Electric Corporation a corporation of Delaware CATHODE HEATER ARRANGEMENT FOR VACUUM TYPE DISPLAY DEVICES 6 Claims, 3 Drawing Figs.

U.S. Cl 315/95, 313/81), 313/108. 313/109.5; 315/101 Int. Cl H0lj 1/72, H01 j 31/06 Field of Search 313/108, 109.5; 315/85, 8.6, 95, 101

References Cited UNITED STATES PATENTS 2,957,098 10/1960 Bernstein 313/109.5X

3l3/109.5X 313/109.5X

6/1964 Crawford etal. 10/1968 DuBois etal. 4.

ABSTRACT: A control circuit for controlling the symbols displayed by a plurality of lamp indicators, each having a cathode and a plurality of phosphor-coated anodles. The control circuit is adapted to control the showing of symbols when similar anodes in all the display devices are connected to a common supply conductor. During the showing of any symbol, the electron-emitting cathode is temporarily disconnected from its power supply by a series transistor. This type of control circuit is particularly adapted to the showing of digital information provided by a computer circuit. The circuit does not employ resistors which produce excessive heat and power consumption.

PULSE aft-#524202 CATI-IODE HEATER ARRANGEMENT FOR VACUUM TYPE DISPLAY DEVICES The present invention relates to a control circuit for showing indicia. While this type if of indicator may be adapted for letters, numerals, and other symbols, the present description will be directed to the showing of digits from zero to nine, inclusive. The invention has particular reference to a control circuit employing a strobing or time-sharing principle. This form of operation results in the saving of manyelectrical circuit components and simplifying the design of the circuit which supplies the digit information.

Many types of digital display devices have been developed and used in connection with the output of computer circuits and other calculating devices. One such device is a lamp having seven segments, each connected as an anode and each coated with a phosphorescent substance which generates light when bombarded by electrons. The device herein described is a diode and employs one or more electron-emitting filaments. There are no control grids of any kind within the evacuated lamp envelope.

One of the features of the present invention is the use of a control circuit which cuts off the filament current during the time the lamp is used as an indicator. At other times the voltage drop across a nonconducting transistor connected in series with the filament increases the voltage of the filament to a value which is substantially equal tothe voltage of the active anodes. While this condition exists, there is no potential from anodes to cathode, and no light is generated.

Another feature of the invention is the absence of resistors in the filament current circuit. Very little heat is generated in the control circuit and less power is required for the operation of the circuit.

For a better understanding of the present invention, together with other details and features thereof, reference is made to the following description taken in connection with the accompanying drawings, of which:

FIG. 1 is a front view of one of the lamps employed as a digit indicator;

FIG. 2 is a schematic diagram of connections showing how three lamps are connected together and to a control circuit for indicating digits; and

FIG. 3 is a graph showing the voltage variations as applied 1 to the three lamps to indicate an array of three numbers 3-1-6 and the filament currents supplied to each of the three lamps during the showing ofinformation.

Referring now to FIG. 1, a digit indicating lamp includes a glass envelope 11 having two filaments 12 and 14 and seven seven signal conductors are used since all similar anodes in each lamp are connected together. When the anodes are to be illuminated they are selectively connected to a grounded conductor 16 while the lamp filaments 12 are coupled through a control circuit to a supply conductor 17 providing a nominal negative potential of -90 volts. Conductors l8 and 20 provide a pulse generator 21 with power and synchronized signals for operating-the lamps. Filament current is applied to the control circuit over conductor 22 which isconnected to each filament in series with a diode 23.

Each control circuit is connected to the lamp filament and includes three transistors 24, 25, 26 and a voltage divider 27. The control circuit associated with lamps 10-1, 10-2, and 10-3 are connected to pulse generator 21 by signal transmitting conductors 28-1, 28-2 and 28-3, respectively. Transistor 24 of each control circuit has its base electrode connected to its respective signal-transmitting conductor, its emitter is connected to ground conductor 16 and its collector is connected through a portion of voltage divider 27 to the base electrode of transistor 25. Transistor 25 has its emitter connected to the negative supply conductor 17 and its collector connected to the base of transistor 26 and to resistor 31 which is connected to ground conductor 16. Transistor 26 has its emitter collector electrodes connected in series between one filament terminal and the negative supply conductor 17. g

The operation of this circuit is as follows: with no signal applied to conductors 28-1, 28-2 and 28-3, from the pulse generator 21, each transistor 24 is conductive and current flows from ground conductor 16, through transistor 24, diode 30, filament 12, diode 23, and back to the power supply 15 over conductor 22. At the same time, current through the voltage divider 27 applies a bias voltage to the base of transistor 25, making it conductive and thereby supplying a virtual short circuit between the base of transistor 26 and its emitter. This action makes each transistor 26 nonconductive, and the filament is disconnected from the negative conductor 17. Under these conditions, the filament voltage is about 2 /2 volts below ground potential. Since the anode voltage is zero, the electric field is too weak to accelerate the electrons emitted by the cathodes 12 and 13 to light the phosphor on the anodes. Thus, each lamp remains dark.

Now, let it be assumed that, in synchronization, the selected combination of anodes of lamp 10-1 (and therefore of the parallel-connected anodes of lamps 110-2 and 10-3) is connected to ground, and a positive-going signal is applied over conductor 28-1 to the base of transistor 24, cutting off conduction through the transistor 24 and thereby blocking the flow of filament current. At the same time, the current through the voltage divider is cut off, transistor 25 is made nonconductive, and transistor 26 is made conductive, connected one end of the filament to the volt conductor 17. The filament still gives off electrons because of its thermal inertia and there is an electric field of 90 volts between the filament and one or more selected anodes 14. The anode coating is bombarded by electrons and the coating gives off light.

It is obvious that the above described condition cannot last too long because the filaments cool off and soon cease to emit electrons. However, it is contemplated to send control signals from circuit 21 having a duration of the order of one-sixtieth of a second. During this time there is no observed cooling effect. Lamps 10-1, 10-2 and 103 are sequentially energized in the manner described above to produce a display of three digits.

It is evident from the above description that the control circuit normally operates the filament at a voltage substantially equal to the anode voltage. When the: lamp is to be lighted, one end of the filament is disconnected from its source of supply and the other end of the filament is connected to a negative voltage. It should be noted that there is no resistor connected in series with the filaments 12 to carry the filament current and generate heat. The only resistors in the control circuit are voltage dividers 27, which consume very little power.

FIG. 3 illustrates the operation of the circuit of FIG. 2 when the number 316 is displayed. During the first time interval from t to Z five anodes B, C, D, F and G in all of the lamps are placed at round or zero potential by the switch circuit 15. Simultaneously, the current through filament 12 of lamp 10-1 is cut off and the filament is placed at a potential of minus 90 volts in the manner described above. Consequently, the figure 3 will be shown by the first lamp. During this first time interval (r to t the filament current in lamps [IO-2 and 10-3 continue to flow, and the filaments of these lamps remain at substantially anode potential. Thus, no display is produced by lamps 10-2 and 10-3.

During the second time interval, from 1 to r the current through filament 12 of lamp 10-2 is cut off, the filament is placed at minus 90 volts, and anode segments A and E are connected to ground or zero potential. Thus, a figure I is displayed by the second lamp while the first and third lamps are unenergized. i

During the third time interval, from to t jthe current through filament 12 of lamp -3 is cut off, the filament is placed at minus 90 volts and anode segments A, B, D, E, F and G are placed at ground or zero potential. Thus, the figure 6 is displayed by lamp 10-3 while the other lamps remain unenergized. This sequential energization of lamps 10-1, 10-2 and 10-3 is repeated at a sufficiently rapid rate to show the number 316 in what appears to the human eye to be a constant (i.e., without blinking or flickering) numerical display.

The advantages of the present invention, as well as certain changes and modifications to the disclosed embodiment thereof, will be readily apparent to those skilled in the art. It is the applicant's intention to cover all those changes and modifications which could be made to the embodiment of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention,

1 claim:

l. A control circuit for repetitively energizing a plurality of indicator lamps in sequence, said lamps each comprising an electron-emissive cathode filament and a plurality of phosphorescent anodes, said control circuit comprising:

a. first circuit means including switching means for sequentially and repetitively applying a predetermined potential to selected groups of anodes in each lamp;

b. second circuit means operative to control the flow of filament current and the filament potential, and including:

1. a first semiconductor switching means which normally passes current to the lamp filament to render it electron-emissive and to maintain the filament at a potential substantially equal to the potential of the anode, and

2. second semiconductor switching means operative to control the cathode-to-anodes potential of each indicator lamp; and

c. signal control circuit means coupled to both the first and second circuit means and operative to render said first semiconductor switching means nonconductive and simultaneously render said second semiconductor switching means conductive, thereby cutting off the filament current and establishing an electric field between the selected anodes and the filament to create an electron flow.

2. A control circuit according to claim 1 .wherein said second circuit means includes a third semiconductor switching means and biasing circuitry associated therewith. coupled between said first and second semiconductor switching means.

3. A control circuit according to claim 2 wherein said first. second and third semiconductor switching means are transistors.

4. A control circuit according to claim 1 wherein the load terminals of said first semiconductor switching means are connected in series with one side of the filament and the load terminals of said second semiconductor switching means are connected in series with the other side of the filament 5. A control circuit according to claim 1 wherein said first circuit means, when connected to a source of electrical power, simultaneously energizes identical combinations of anodes in all of said lamps and said second circuit means places an electron-accelerating potential between the filament and the combination of anodes of the selected lamps.

6. A control circuit according to claim 1 in combination with a plurality of indicator lamps, each lamp comprising an electron-emissive filament and seven phosphor-coated anodes arranged in a figure eight pattern for forming the digits from O to 9, inclusive. 

1. A control circuit for repetitively energizing a plurality of indicator lamps in sequence, said lamps each comprising an electron-emissive cathode filament and a plurality of phosphorescent anodes, said control circuit comprising: a. first circuit means including switching means for sequentially and repetitively applying a predetermined potential to selected groups of anodes in each lamp; b. second circuit means operative to control the flow of filament current and the filament potential, and including:
 1. a first semiconductor switching means which normally passes current to the lamp filament to render it electron-emissive and to maintain the filament at a potential substantially equal to the potential of the anode, and
 2. second semiconductor switching means operative to control the cathode-to-anodes potential of each indicator lamp; and c. signal control circuit means coupled to both the first and second circuit means and operative to render said first semiconductor switching means nonconductive and simultaneously render said second semiconductor switching means conductive, thereby cutting off the filament current and establishing an electric field between the selected anodes and the filament to create an electron flow.
 2. second semiconductor switching means operative to control the cathode-to-anodes potential of each indicator lamp; and c. signal control circuit means coupled to both the first and second circuit means and operative to render said first semiconductor switching means nonconductive and simultaneously render said second semiconductor switching means conductive, thereby cutting off the filament current and establishing an electric field between the selected anodes and the filament to create an electron flow.
 2. A control circuit according to claim 1 wherein said second circuit means includes a third semiconDuctor switching means and biasing circuitry associated therewith, coupled between said first and second semiconductor switching means.
 3. A control circuit according to claim 2 wherein said first, second and third semiconductor switching means are transistors.
 4. A control circuit according to claim 1 wherein the load terminals of said first semiconductor switching means are connected in series with one side of the filament and the load terminals of said second semiconductor switching means are connected in series with the other side of the filament
 5. A control circuit according to claim 1 wherein said first circuit means, when connected to a source of electrical power, simultaneously energizes identical combinations of anodes in all of said lamps and said second circuit means places an electron-accelerating potential between the filament and the combination of anodes of the selected lamps.
 6. A control circuit according to claim 1 in combination with a plurality of indicator lamps, each lamp comprising an electron-emissive filament and seven phosphor-coated anodes arranged in a figure eight pattern for forming the digits from 0 to 9, inclusive. 